Heading to Mars? Save room for three tons of food. That's about how much you'll need to feed a crew of four during an 18-month trip.

Or, you could harvest your own crops from a space greenhouse, like the prototype unit NASA is testing in Arizona this month during its space technology lollapalooza known as Desert RATs.

A team from Kennedy Space Center is tending to the greenhouse, with the goal of getting the system ready for a test run aboard the International Space Station. The unit, built by Wisconsin-based Orbital Technologies Corp., is designed to be lightweight, energy- efficient and very low maintenance.

Light for the plants comes from a combination of red, green and blue LEDs. The growing medium contains seeds and time-release fertilizer. Water wicks passively through the system.

The chamber, roughly 16 by 20 inches, is collapsible, so that when the seeds are just beginning to grow, the lights are very close to the rooting mat. The unit expands to accommodate the plants as they grow.

"It has held up very well," NASA's lead scientist Ray Wheeler wrote in an email to Discovery News. "We didn't have any failures e.g., water leaks, electrical overloads, plants drying out, etc.), which is all important information for assessing the system reliability."

During the test run in Arizona, three types of lettuce were grown in the chamber and consumed by study participants.

"We are interested in their comments, as well as their thoughts on just having … green, living plants in an otherwise very mechanical and engineering setting," Wheeler added.

The system has been under development intermittently for more than decade, depending on funding. During that time, Orbital Technologies was able to reduce the system's power requirements to around 100 watts.

"The majority of the hardware revolves around the lighting system. It's very efficient," Orbital Technologies project manager Robert Richter told Discovery News.

The LEDs only emit wavelengths of light that are used by the plants, primarily blue light for plant structure and orientation in microgravity, and red light for photosynthesis.

In addition to lettuce and other leafy greens, tomatoes, radishes, dwarf green peppers and aromatic herbs, such as basil and mint, are candidate space crops, said Orbital Technologies biologist Robert Morrow.

Initial tests show the nutritional value of the vegetables is similar to terrestrial-grown plants. NASA plans additional studies to make sure plants won't introduce food-borne pathogens into the station.

For longer flights, such as a trip to Mars, Richter envisions a space greenhouse the size of a station module to feed the crew — in body and spirit.

"It's a psychological boost," Richter said. "Whenever we have had a plant science payload, the station crew was going over several times a day to see the plants."

"I think it has applications on Earth as well, like aboard submarines," he added. "Anywhere you're removed from the environment and you need effective use of power to grow plants."

Related research programs focus on using plants to regenerate air and process water, in addition to providing food. The University of Arizona, for example, is testing an 18- by 7-foot greenhouse that's producing sweet potatoes, lettuce, tomatoes and strawberries — enough to provide half the calories for one astronaut and all his or her fresh water and oxygen.